The influence of the quality of ferrosilicon on the rheology of dense medium and the ability to reach higher densities

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1 The influence of the qulity of feosilicon on the heology of dense medium nd the bility to ech highe densities by H.A. Mybugh* J o u n l Synopsis The dense medium beneficition of hevy metl oxide oes such s ion oe is usully done by hevy medium seption in cyclones, sttic bths (Wemco dum) nd nowdys with Lcodems. At Sishen Ion Oe Mine the fist Lcodem ws instlled to beneficite ion oe nd good compison cn be mde between the Lcodem nd Wemco dum fte thee-ye poduction peiod. A compison will be mde in this ppe on the poduction pefomnce of the Lcodem ginst the Wemco dum concentting on the thoughput nd the high densities of 4.2 chieved. Pefomnce poblems encounteed duing the commissioning of the Lcodem nd the ectifiction will be discussed s well s the poduction cost. The flow lines of the Lcodem module will be discussed nd specil emphses will be put on the chnges mde fte commissioning to be ble to keep the votex in the Lcodem constnt t density of 4.2. All the dvntgeous nd disdvntgeous will be listed. Intoduction The beneficition of hevy metl oxides, such s ion oe, is usully pefomed with hevy medium seption in cyclones, sttic bths nd ltely with Lcodems. Atomized feosilicon is most suitble s hevy medium t densities bove kg/m3 whees mixtue of milled nd tomized feosilicon is suitble t densities below kg/m3. When beneficition plnt is opeted t densities highe thn 3600 kg/m3, the qulity of the feosilicon pticles is n impotnt fcto tht influences the contol of the beneficition pocess. Theefoe, it is impotnt to know how the heology would be ffected by the feosilicon qulity s it lso influences the contol of the pocess t these elevted densities. Bckgound The Kumb Resouces Sishen Ion Oe Mine in South Afic poduces 26.5 Mt ion oe pe nnum fom its beneficition plnt. The oebody consists minly of lminted nd mssive type hemtite oe tht is cushed down to 90 mm befoe being beneficited by mens of combintion of Wemco dums, Lcodem nd dense medium cyclone septos. The need fo highe densities When the pecentge of high-density gngue2 is highe thn noml in the un-of-mine (ROM), highe seption density is necessy to poduce poduct to specifiction. Cetin oe types of this qulity in the Sishen eseves equie septing density highe thn kg/m3, whees densities would nomlly vege kg/m3 when beneficiting oes of noml high-density gngue content. Sink nd flot tests conducted on the ROM mteil t Sishen eveled some inteesting chcteistics. In the wste fction (density < kg/m3), it ws found tht the %Fe ws <21% (Figue 1). Similly, fo the poduct fction (density >3 000 kg/m3), the pecentge Fe vied between 35% nd 67.2%. The bulk of the mteil (88%) ctully hd density gete thn kg/m3 nd Fe content tht vied between 63% nd 67.2%. At density intevl of to kg/m3, the Fe content vied fom 37% to 60% with n vege of 45%. The question of whethe o not the finl poduct will meet the qulity specifiction is lgely dependent on the mss pecentge of * Sishen Ion Oe Mine, Kumb Resouces. The Southen Aficn Institute of Mining nd Metllugy, SA ISSN X/ This ppe ws fist published t the SAIMM Confeence, DMS nd gvity concenttion opetions nd technology in South Afic, July P p e The Jounl of The Southen Aficn Institute of Mining nd Metllugy VOLUME 106 NON-REFEREED PAPER NOVEMBER

2 The influence of the qulity of feosilicon %Fe Reltive density of minel Figue 1 Pecentge Fe in diffeent pticle densities Mss pecentge Reltive density of pticles Figue 2 Mss pe cent distibution by pticle density of finl poduct pticles with pticle density in the nge kg/m3 to 4000 kg/m3 tht epots to the poduct. The mss pecentge ws found to vy fom 0.8% to 9% (Figue 2) with n vege of 3.2%. The Fe specifiction of the lumpy oe poduct (-25 mm + 8 mm) t Sishen is >66%. If the ne density mteil1 exceeds 6%, it becomes difficult to ech the poduct Fe specifiction. Nomlly the ne density mteil in the ROM cn be educed by loweing the tio of mteil mined in es known to contin high pecentge of ne density mteil. On occsion, when this is not possible, the only mens of poducing poduct to specifiction is to incese the opeting densities duing the beneficition pocess. In the pst, eching nd monitoing densities highe thn kg/m3 poved difficult, due to incesed medium viscosity tht influenced the beneficition chcteistics, mking it difficult to pump the medi. Rheology of the medium The heology of the medium is influenced by fou fctos, nmely: medium density, pecentge slimes (% -200 µm non mgnetic mteil), feosilicon pticle spheicity nd the pecentge feosilicon pticles tht e smlle thn 45 µm (Figue 3). At ciculting densities below kg/m3 the opeting nge of these fctos ovelp to such n extent 728 NOVEMBER 2006 VOLUME 106 NON-REFEREED PAPER The Jounl of The Southen Aficn Institute of Mining nd Metllugy

3 The influence of the qulity of feosilicon tht lge opeting window fo the medium cicuit exists. With n incese in ciculting density the opeting window becomes smlle nd the influence tht these vibles hve on the pocess becomes moe ppent. Theefoe, it is citicl tht ll the fctos mentioned bove tht influence the medium e mesued on egul bsis if the pocess is pone to opete t highe densities. These citicl fctos influence the pocess in the sense tht they cn incese viscosity o cuse instbility of the dense medium. Figue 3 Schemtic explntion of vibles on heology of medium Degdtion of feosilicon pticles in the dense medium With the stndd stem tomized feosilicon, density of kg/m3 ws eched on cetin occsions but it ws only possible to sustin constnt density of kg/m3. Densities bove kg/m3 cused vey high viscosity poblems tht influenced the chcteistics of the beneficition pocess. The only popety tht could be contolled t tht stge ws the pecentge slime pesent in the ciculting coect medium. The plnt ws set up in such wy tht most of the slimes could be emoved fom the ciculting medi, which helped in chieving density of kg/m3. All the fctos tht could influence the high viscosity sitution wee exmined. These included density of medium, mount of slimes, spheicity of medi nd the pecentge -45 µm feosilicon medi. The cceptble mount of -45 µm feosilicon pticles equied to chieve the coect diffeentil in the cyclone nd dum plnt espectively is 62% nd 55% lthough only feosilicon medi with -45 µm pecentge less thn 20% ws dded to the cicuit. Smples tken of the coect medi indicted tht the pecentge 45 µm incesed to 75% (Figue 4). This is one of the citicl fctos tht influence viscosity nd stbility t Sishen, nd the elevted vlues led to high viscosities t medium densities bove kg/m3. Thus, emovl of excess slimes fom the coect medium did not eliminte the viscosity poblem. In fct the incese in the fine feosilicon fction ctully contibuted to gete degee to the incesed viscosity. Investigtion showed tht the cuse of the degdtion ws cused by combintion of the tomising pocess nd the w mteils used to poduce the feosilicon pticles. In the stndd pocess, stem is used to tomize the feosilicon nd the high pecentge fee cbon in the w mteil is believed to hve ected to fom gses, esulting in hollow pticles nd gin boundy poosity (Figues 5 nd 6). These pticles (the hollow nd the smlle solid pticles) e then degded duing the beneficition pocess, esulting in n incese in the pecentge -45 µm fction nd loweing of the spheicity (Figues 7, 8, 9 nd 10) of the feosilicon pticles in cicultion. J o u n l P p e Old feosilicon vs. new feosilicon % -45 µm FeSi Time Figue 4 The incese of the fine fction feosilicon in the coect medium The Jounl of The Southen Aficn Institute of Mining nd Metllugy VOLUME 106 NON-REFEREED PAPER NOVEMBER

4 The influence of the qulity of feosilicon Figue 5 Hollow pticles in unused feosilicon Figue 8 Degded pticles in the medi Figue 6 Gin boundy poosity in unused feosilicon Figues 9 Solid pticles stted to degde in the ciculting medi Figue 7 Hollow pticle with gin boundy poosity Figues 10 Solid pticles stted to degde in the ciculting medi 730 NOVEMBER 2006 VOLUME 106 NON-REFEREED PAPER The Jounl of The Southen Aficn Institute of Mining nd Metllugy

5 The influence of the qulity of feosilicon Figue 11 Used feosilicon showing the spheicity poblem The degded pticles thus incesed the pecentge of the -45 µm feosilicon fction up to 75%. This is believed to be one of the fctos tht incesed the viscosity of the ciculting medi. The degdtion of the pticles lso cused decese in the spheicity of the ciculting medi nd thus contibuted to n incese in the viscosity of the medi (Figue 11). The decesed spheicity of the feosilicon pticles in the coect medi mkes it moe difficult to emove the slimes fom the ciculting medi nd this gin inceses the viscosity. It becme ppent tht n ltetion to the physicl popeties of the feosilicon, i.e. impove spheicity, ws necessy to ech sustinble densities exceeding kg/m3. A feosilicon with no hollow pticles nd no gin boundy poosity would theefoe be the idel to un the plnt t highe densities. The impoved feosilicon A pocess tht uses nitogen to tomize the feosilicon nd w mteil with vey low cbon content (0.02% C mx) ws found nd dopted by Kumb Resouces. The new pocess thus eliminted the poblems cused by the pevious tomiztion pocess, thus llowing the plnt to chieve highe densities. The intoduction of the new feosilicon to the plnt esulted in significnt chnge in opeting conditions. The pevious viscosity poblem then chnged to n instbility poblem nd ll sfeguds tht wee built into the plnt to ovecome the viscosity poblem hd to be chnged to ovecome the stbility poblem. Poblems with the impoved feosilicon The impoved feosilicon cused some new poblems in the plnt. With time, s the new feosilicon ws intoduced to the plnt, the viscosity poblem chnged into stbility poblem. The new feosilicon did not lose its spheicity with time nd no degdtion of the pticles occued (Figue 12). Tests showed tht the new feosilicon pticles did not bek down nd thus etined thei spheicity. The spheicl pticles did not hinde the emovl of the slimes though the densifies. This esulted in low pecentge slimes (0.8%) in the ciculting medi. The culmintion of ll these fctos decesed the viscosity to such n extent tht the plnt ws in stte of instbility. The beneficition chcteistics wee influenced nd mny chnges hd to be mde. All the chnges tht wee in plce to emove the excess slimes hd to be chnged bck to keep s much slimes s possible in the plnt. These chnges mde it possible to incese the pecentge slimes to between 6% nd 8% nd mde the contol in the plnt cceptble. The instbility of the medium ppeed to wosen fte polonged poduction. The impoved feosilicon, howeve, possessed ovell bette spheicity, which esulted in bette slime contol in the ciculting medi. Whees the specifiction of the -45 µm fction fo the old feosilicon ws between 0% nd 20%, fo the new feosilicon it ws incesed to between 45% nd 55% fo the dum plnt nd 55% nd 65% fo the cyclone plnt (Figue 13). A few tests did evel though tht the -45 µm feosilicon fction in the ciculting medi dopped s low s 22% (Figue 13). This vey low pecentge of the fine fction of feosilicon in the ciculting medi cused instbility in the ciculting medi nd needed to be ectified. Afte mny chnges in the wy the pocess ws contolled, optimum esults wee chieved by incesing the density to kg/m3 nd highe. This kept the plnt unning but still thee ws instbility in the pocess due to the loweed fine fction. Figue 12 Impoved feosilicon pticles showing the spheicity nd tht no bekdown occued fte six months in the plnt J o u n l P p e The Jounl of The Southen Aficn Institute of Mining nd Metllugy VOLUME 106 NON-REFEREED PAPER NOVEMBER

6 The influence of the qulity of feosilicon Figue 13 The decese of the fine fction feosilicon in the coect medium with the new feosilicon Tble I Distibution of fine feosilicon pticles in plnt % -45 µm % -45 µm % -45 µm Apptus in feed in undeflow in oveflow Mgnetic septo 78% 40% 5% Poduct sceens 45% 5% 55% Wste sceen 45% 5% 25% Densifie 52% 1% 96% Loss of the fine feosilicon fction It is well known tht the loss of feosilicon occus minly t the poduct nd wste sceen oveflow nd t the secondy mgnetic septo. It ws genelly ccepted tht the complete fctionl distibution of the feosilicon pticles is lost eqully duing the beneficition pocess. Smples wee tken in the plnt t diffeent flow lines nd nlyses. Out of these nlyses it ws cle tht the fine fction feosilicon pticles e concentted in the dilute medium. Loss of feosilicon ove the poduct sceen nd the mgnetic septo is mostly of the fine fction. The loss of the fine fction of feosilicon esulted in the low (22%) pecentge of feosilicon ciculting in module cusing n unstble medium tht influenced the beneficition chcteistics nd cused opetionl poblems. The highe densities helped to contol the plnt but the spy wte on the poduct nd wste sceens hd to be impoved to keep the loss of the fine fction to minimum ove the sceens. New mgnetic septos wee instlled to ecove moe of the feosilicon. The opeting pocedues of the ltte wee eviewed nd impovements wee mde to thei efficiency by mintining constnt feed t the coect concenttion of feosilicon. The fctos mentioned bove cused n incese in the fine feosilicon fction of the medi to 40% nd esulted in moe contollble plnt by keeping the density bove kg/m3. With new medi flow line developed fo the Lcodem, dum plnt nd cyclone plnt, highe densities cn be mintined nd density of kg/m3 ws eched on occsion nd kg/m3 ws esily mintined in the Lcodem cicuit. Conclusion When opeting beneficition plnt t eltive densities highe thn kg/m3 the qulity of the feosilicon pticles is n impotnt fcto tht influences the contol of the beneficition pocess. The following spects e extemely impotnt if densities bove kg/m3 e needed in beneficition plnt, nmely: shpe of the pticle, physicl stength of feosilicon pticle, the pecentge -45 µm feosilicon pticles nd pecentge slimes. By intoducing the impoved feosilicon to ovecome the viscosity poblem occuing t densities fom kg/m3 nd highe, stbility poblem might occu tht must be ovecome befoe stble medi fo noml poduction cn be chieved. The getest chievement fom ll the chnges tht wee mde ws the bility to ech nd mintin the highe densities of kg/m3. This ws only possible due to the chnges mde to the metllugicl chcteistics of the feosilicon. With new medi flow line developed, specificlly fo the impoved feosilicon, density bove kg/m3 could esily be eched nd kg/m3 cn be mintined. Instbility poblems tht esulted due to the loss of fine feosilicon pticles, peviously non-ppent to the degdtion of cose pticles to eplce fine losses, wee ovecome by chnging the flow line nd lteing the specifiction fo the impoved feosilicon to highe pecentge -45 µm pticle. Refeences 1. GROBLER, J. Mnge Feosilicon Plnt Pivte Communiction. 2. Pivte Communictions with Feosilicon Tem t Sishen Ion Oe Mine. 3. MYBURGH, H.A. Sishen Ion Oe Mine, Combintion of in-house epots. 732 NOVEMBER 2006 VOLUME 106 NON-REFEREED PAPER The Jounl of The Southen Aficn Institute of Mining nd Metllugy